1. Field of the Disclosure
The disclosure relates generally to methods for processing substrates carrying coatings comprising a metal. More particularly, the disclosure is directed to methods of processing substrates, such as medical devices, carrying coatings comprising a metal and having antimicrobial activity.
2. Brief Description of Related Technology
Even brief exposure to surfaces contaminated with microbes can introduce bacterial, viral, fungal, or other undesirable infections to humans and other animals. Of particular concern is preventing or reducing microbial infection associated with the use of invasive medical devices such as catheters, intravenous fluid administration systems, and other medical devices which require prolonged patient contact and thus present significant infection risks. Contamination may result from the patients' own flora or from one or more healthcare workers' hands during insertion and/or manipulation of the device, or from both the patient and the healthcare worker. Medical devices coated with antimicrobial materials can reduce the transfer of such microbes to patients, thereby improving the safety and efficacy of these devices. Such antimicrobial coatings often include silver metal or silver salts, or other metals with demonstrable antimicrobial activity such as copper, gold, zinc, cerium, platinum, palladium, or tin.
Silver and salts thereof are commonly used in antimicrobial coatings because of their demonstrated broad spectrum antimicrobial activity against various bacteria, viruses, yeast, fungi, and protozoa. It is theorized that the observed antimicrobial activity is primarily due to the ability of silver ions to tightly bind nucleophilic functional groups containing sulfur, oxygen or nitrogen. Many nucleophilic functional groups such as thiols, carboxylates, phosphates, alcohols, amines, imidazoles, and indoles are prevalent in biomolecules. Upon binding of ionized silver to these various nucleophilic functional groups, it is believed that widespread disruption and inactivation of microbial biomolecules (and thus antimicrobial activity) occurs.
Silver and salts thereof have therefore been used as antimicrobial agents in a wide variety of applications; for example, they have been incorporated in the absorbent materials of wound care products such as dressings, gels, and bandages, and also in compositions for providing antimicrobial coatings on medical devices. One disadvantage of some metallic silver-containing antimicrobial coatings, however, is their color/opaqueness, which prevents a healthcare provider from being able to see through the medical device substrate. Coatings comprising metallic silver, for example, can be brown in color. Thus, when such colored coatings are applied to transparent surfaces, the coated surfaces typically have a brown color and significantly diminished transparency.
In contrast to coatings comprising metallic silver, many coatings comprising silver salts are transparent or translucent, and/or lack a colored appearance. Thus, when silver salt coatings are applied to transparent surfaces, the coated surfaces typically have little color and are highly transparent. While coatings comprising silver salts are often translucent, it is extremely difficult to solubilize silver salts and thus to directly deposit coatings comprising silver salts.